Chaminda Hettiarachchi | University of South Florida (original) (raw)

Papers by Chaminda Hettiarachchi

Research paper thumbnail of Growth and Characterization of PEDOT:PSS and Carbon Nanotube Composite Structures for Excitonic Solar Cells

Harnessing solar energy is one of the most promising ways to tackle today's energy issues. Th... more Harnessing solar energy is one of the most promising ways to tackle today's energy issues. Though solar cells are comprised of many different layers, our focus is on a single layer. The main goal of this study is to create thin film composite structures of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and carbon nanotubes (CNT), more specifically with multiple wall carbon nanotubes (MWCNT) by employing a spray method that utilizes Bernoulli's principle. We believe that a spray method will produce a better uniform layer than other methods that are utilized for creating thin films. Uniformity within a thin film is of the upmost importance because as uniformity is improved, many properties are enhanced. PEDOT:PSS was mixed separately with both dimethylformamide (DMF) and water. By the Dektak 3030ST, a profilometer device, it was discovered that the PEDOT:PSS containing DMF dispersed better than the PEDOT:PSS mixed with water, thus creating a more uniform f...

Research paper thumbnail of Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

Physical Review B, 2010

The electronic properties of single- and multication transparent conducting oxides (TCOs) are inv... more The electronic properties of single- and multication transparent conducting oxides (TCOs) are investigated using first-principles density-functional approach. A detailed comparison of the electronic band structure of stoichiometric and oxygen deficient In2O3 , α , and β-Ga2O3 , rock salt and wurtzite ZnO, and layered InGaZnO4 reveals the role of the following factors which govern the transport and optical properties of these TCO materials: (i) the crystal symmetry of the oxides, including both the oxygen coordination and the long-range structural anisotropy; (ii) the electronic configuration of the cation(s), specifically, the type of orbital(s)— s , p , or d —which form the conduction band; and (iii) the strength of the hybridization between the cation’s states and the p states of the neighboring oxygen atoms. The results not only explain the experimentally observed trends in the electrical conductivity in the single-cation TCO, but also demonstrate that multicomponent oxides may offer a way to overcome the electron localization bottleneck which limits the charge transport in wide band-gap main-group metal oxides. Further, the advantages of aliovalent substitutional doping—an alternative route to generate carriers in a TCO host—are outlined based on the electronic band structure calculations of Sn, Ga, Ti, and Zr-doped InGaZnO4 . We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.

Research paper thumbnail of Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

Physical Review B, 2010

The electronic properties of single- and multi-cation transparent conducting oxides (TCOs) are in... more The electronic properties of single- and multi-cation transparent conducting oxides (TCOs) are investigated using first-principles density functional approach. A detailed comparison of the electronic band structure of stoichiometric and oxygen deficient In$_2$O$_3$, alpha\alphaalpha- and beta\betabeta-Ga$_2$O$_3$, rock salt and wurtzite ZnO, and layered InGaZnO$_4$ reveals the role of the following factors which govern the transport and optical properties of these TCO materials: (i) the crystal symmetry of the oxides, including both the oxygen coordination and the long-range structural anisotropy; (ii) the electronic configuration of the cation(s), specifically, the type of orbital(s) -- sss, ppp or ddd -- which form the conduction band; and (iii) the strength of the hybridization between the cation's states and the p-states of the neighboring oxygen atoms. The results not only explain the experimentally observed trends in the electrical conductivity in the single-cation TCO, but also demonstrate that multicomponent oxides may offer a way to overcome the electron localization bottleneck which limits the charge transport in wide-bandgap main-group metal oxides. Further, the advantages of aliovalent substitutional doping -- an alternative route to generate carriers in a TCO host -- are outlined based on the electronic band structure calculations of Sn, Ga, Ti and Zr-doped InGaZnO$_4$. We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.

Research paper thumbnail of Growth and Characterization of PEDOT:PSS and Carbon Nanotube Composite Structures for Excitonic Solar Cells

Harnessing solar energy is one of the most promising ways to tackle today's energy issues. Th... more Harnessing solar energy is one of the most promising ways to tackle today's energy issues. Though solar cells are comprised of many different layers, our focus is on a single layer. The main goal of this study is to create thin film composite structures of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and carbon nanotubes (CNT), more specifically with multiple wall carbon nanotubes (MWCNT) by employing a spray method that utilizes Bernoulli's principle. We believe that a spray method will produce a better uniform layer than other methods that are utilized for creating thin films. Uniformity within a thin film is of the upmost importance because as uniformity is improved, many properties are enhanced. PEDOT:PSS was mixed separately with both dimethylformamide (DMF) and water. By the Dektak 3030ST, a profilometer device, it was discovered that the PEDOT:PSS containing DMF dispersed better than the PEDOT:PSS mixed with water, thus creating a more uniform f...

Research paper thumbnail of Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

Physical Review B, 2010

The electronic properties of single- and multication transparent conducting oxides (TCOs) are inv... more The electronic properties of single- and multication transparent conducting oxides (TCOs) are investigated using first-principles density-functional approach. A detailed comparison of the electronic band structure of stoichiometric and oxygen deficient In2O3 , α , and β-Ga2O3 , rock salt and wurtzite ZnO, and layered InGaZnO4 reveals the role of the following factors which govern the transport and optical properties of these TCO materials: (i) the crystal symmetry of the oxides, including both the oxygen coordination and the long-range structural anisotropy; (ii) the electronic configuration of the cation(s), specifically, the type of orbital(s)— s , p , or d —which form the conduction band; and (iii) the strength of the hybridization between the cation’s states and the p states of the neighboring oxygen atoms. The results not only explain the experimentally observed trends in the electrical conductivity in the single-cation TCO, but also demonstrate that multicomponent oxides may offer a way to overcome the electron localization bottleneck which limits the charge transport in wide band-gap main-group metal oxides. Further, the advantages of aliovalent substitutional doping—an alternative route to generate carriers in a TCO host—are outlined based on the electronic band structure calculations of Sn, Ga, Ti, and Zr-doped InGaZnO4 . We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.

Research paper thumbnail of Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

Physical Review B, 2010

The electronic properties of single- and multi-cation transparent conducting oxides (TCOs) are in... more The electronic properties of single- and multi-cation transparent conducting oxides (TCOs) are investigated using first-principles density functional approach. A detailed comparison of the electronic band structure of stoichiometric and oxygen deficient In$_2$O$_3$, alpha\alphaalpha- and beta\betabeta-Ga$_2$O$_3$, rock salt and wurtzite ZnO, and layered InGaZnO$_4$ reveals the role of the following factors which govern the transport and optical properties of these TCO materials: (i) the crystal symmetry of the oxides, including both the oxygen coordination and the long-range structural anisotropy; (ii) the electronic configuration of the cation(s), specifically, the type of orbital(s) -- sss, ppp or ddd -- which form the conduction band; and (iii) the strength of the hybridization between the cation's states and the p-states of the neighboring oxygen atoms. The results not only explain the experimentally observed trends in the electrical conductivity in the single-cation TCO, but also demonstrate that multicomponent oxides may offer a way to overcome the electron localization bottleneck which limits the charge transport in wide-bandgap main-group metal oxides. Further, the advantages of aliovalent substitutional doping -- an alternative route to generate carriers in a TCO host -- are outlined based on the electronic band structure calculations of Sn, Ga, Ti and Zr-doped InGaZnO$_4$. We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.